The present invention relates generally to improved position, distance measuring, navigation, and information systems for use on golf courses, and more particularly to improved components for a golf navigation system utilizing dead reckoning.
In golf, players are more comfortable and more likely to excel on courses with which they are familiar. It is customary for a golfer on a new or little-played course to seek to gain at least some familiarity with the layout of each hole before starting play. Armed with this information, the golfer can approach each tee box during play of the course, knowing, for example, whether the particular hole is a xe2x80x98dog leg leftxe2x80x99, a xe2x80x98dog leg rightxe2x80x99, or straight; the general locations of hazards, such as sand traps, bunkers, and water traps on the hole; and locations of range postings, if any, for calculating yardage from the golfer""s location to the front and rear of the green, the pin (cup), a hazard, and a desired lay up position for the green approach shot.
Golf courses have traditionally made available course layout and feature information booklets in the pro shop, for just such purposes. Yardage markers typically are placed at sprinkler heads along each hole, to provide range information from that point to the center of the green. These serve as aids to the player, but they also contribute to slowing the pace of play of the course. Slow play has an adverse effect on the courses daily revenue, as well as on other golfers"" enjoyment of the game.
Proposals made to improve golf course information systems include use of buried electrical wires in various layouts on the course for interaction with mobile overland components (e.g., U.S. Pat. No. (USPN) 5,044,634 (xe2x80x9cthe ""634 patentxe2x80x9d); and use of radio direction finding or triangulation techniques (e.g., USPN 4,703,444 (xe2x80x9che ""444 patentxe2x80x9d) and USPN 5,056,106).
More than twenty years ago, the U.S. government established a Global Positioning System (GPS) that uses space satellites and ground based stations to determine distance, range, and position, primarily for defense purposes, but which has found many uses for such information in various industrial and commercial applications. Earth-orbiting satellites provide reference points from which to determine the position of a point on or near the earth, using ground-based receivers. The satellite orbits are monitored by the ground station GPS receivers, and the travel times of signals received from the satellites are used to measure distance to each satellite. Each signal from a satellite is coded to permit the receiver to determine the elapsed time between transmission of the signal from the respective satellite and reception at the GPS receiver antenna, and thereby to calculate the distance as the product of elapsed time and speed of light. Receivers are not restricted to large ground stations, but may be portable, mobile and hand-held units for a multitude of private navigation, position and distance-measuring systems.
Distance measurements to three GPS satellites are used to accurately define the position of an object such as a GPS receiver, which may be stationary or moving, on or near the earth""s surface. A fourth satellite enables verification of clock timing in the GPS system. With several satellites in xe2x80x9cviewxe2x80x9d (i.e., line-of-sight, or LOS), and using a computer, distances between objects can theoretically be measured almost instantaneously with great accuracy. But as a practical matter even small errors that typically occur in the calculated measurement of satellite signal travel time from system and natural phenomena can substantially reduce the accuracy of the distance and position calculations. Error causing phenomena include atmospheric propagation, receiver contributions, satellite ephemeris, and satellite clock. Errors have been purposely introduced in the satellite signals by the government to deny civilian users full accuracy. The combined effect of these errors can be as high as 100 meters or so.
In co-pending patent application Ser. Nos. 08/423,295 (now U.S. Pat. No. 5,689,431) and 08/525,905, filed Apr. 18, 1995 and Sep. 8, 1995, respectively, assigned to the same assignee as the present application (xe2x80x9cThe ""295 and ""905 applicationsxe2x80x9d), improvements are disclosed in golf course positioning and yardage measuring systems utilizing differential GPS (DGPS) (see, for example, Blackwell, xe2x80x9cOverview of Differential GPS Methodsxe2x80x9d, Global Positioning System, vol. 3, pp. 89-100, The Institute of Navigation, Washington, D.C. (1986)). With DGPS, errors in distance measuring applications are reduced by broadcasting error correction information from a ground receiver of known location in the vicinity of the user. The difference between a known fixed position of a GPS receiver and its position calculated from the satellite GPS signal fixes the error in the signal, and a continuous correction is provided for all other receivers, fixed or mobile, in the reception area. Knowing the error allows all distance and position calculations at the user""s receiver to be corrected.
The golf course positioning and yardage measuring systems of the ""295 and ""905 applications use unique filtering algorithms, among other things, to offer much greater accuracy and reliability than are found with conventional DGPS systems. An efficient, yet inexpensive communications network is used for data transmission between a base station and golf carts, with a variable length communication network that allows golf carts to be readily added or removed from the network. Other advantages include detecting when the golf cart is within predetermined zones or regions of the course for use in unique features such as automatic display of the current hole on the cart monitor, measuring the pace of play for each hole, and providing automatic pop-up golf tips and advertisements on the cart monitor as the cart transitions from one hole to the next. The monitor is mounted in the roof of the cart in a way that gives the user excellent color readability in sunlight.
The PROLINK(trademark) yardage and course management system disclosed in the ""295 and ""905 applications (PROLINK is a trademark of PROLINK, INC. of Chandler, Ariz., the assignee of the invention disclosed herein and in the ""295 and ""905 applications) includes a golf cart-based subsystem (or, alternatively, a hand-held or other roving unit) that uses state-of-the-art DGPS technology, coupled with specialized hardware and software. The system creates, stores, and displays a color graphical representation or map of the golf course on a video monitor or liquid crystal display (LCD) in the cart. Each hole of the course is selectively displayed with all of its hazards and features, with an icon representing the fixed or changing position of the roving unit superimposed in real time on the map of the hole being played. The golfer is provided by the system with an accurate measurement of the distance from the current position of the cart (e.g., at the tee box or other location on the hole) to the current pin placement, a hazard, or any other feature of the hole.
The PROLINK system provides many advantages to the golfer without burdening or significantly changing the way the course or any particular hole is played, or how business is conducted by course managementxe2x80x94advantages such as real-time, accurate indications of distance (typically within two meters) from the cart to significant course features xe2x80x94green, pin, hazards on fairway, etc.; a relatively large, high resolution, color display with the capability for selection of a map of the entire course or any individual hole or other detailed feature; and a capability of individualized communications and messaging to and from the cart. The hole display and yardage functions in the cart system are activated automatically as the cart approaches the tee box at commencement of play of each hole. A movable cursor on the display allows the player to point to any feature on the displayed map to obtain a precise yardage measurement from the position of the cart. An automatic zoom feature increases the selected target area resolution, such as to view the contour of the green or the details of a particular hazard. The PROLINK system also enables the player to make consistently better and faster club selection from the information concerning target distance and hole layout.
The course management portion of the PROLINK system includes a base station computer unit, receiver/transmitter unit and video monitor in the clubhouse (or other desired location) to give the course administrator better insight into daily operations and revenues by providing a capability to identify, locate and monitor movement of every golf cart on the course in real-time; to use that knowledge to pinpoint and analyze the cause of bottlenecks on the course; to compile an extensive computerized data base useful for statistical insight into course operations and techniques for instituting improvements; and to communicate with all carts on the course, and to enhance course revenues through advertising and promotions broadcast to the cart monitors.
The PROLINK system also employs a technique and method for collecting survey data to map the layout of the golf course including such features as tee boxes, greens, fairways, cart paths, water hazards and sand traps. The collected survey data is post-processed and efficiently stored in memory in vector form for later retrieval and display. This data representing the golf course layout is used to efficiently determine the location of a golf cart relative to predetermined zones or regions.
Despite the capabilities of GPS and DGPS systems for their intended purpose, in golf course and other positioning, distance measuring, and ranging applications, such systems suffer loss of signal and, therefore, loss of communication and capability, when the roving unit moves behind an obstruction. On the golf course, this is particularly troublesome where the course is heavily treed, or has hilly terrain, or has on-course or adjacent buildings or other structures, or all of these types of obstructions, of sufficient dimensions to obscure or interfere with strong signal transmission. In these conditions, the golfer is inevitably faced with an xe2x80x9cout-of-servicexe2x80x9d display screen on the cart monitor.
Co-pending U.S. patent application Ser. No. 08/690,962 titled xe2x80x9cRobust Golf Navigation Systemxe2x80x9d filed Aug. 1, 1996 in the names of J. Coffee et al. and commonly assigned with this application (hereinafter xe2x80x9cthe ""962 applicationxe2x80x9d) discloses a dead reckoning system that overcomes these problems. The ""962 application is incorporated in its entirety herein, by reference. The ACUTRAK(trademark) golf course yardage and information system (ACUTRAK is a trademark of PROLINK, INC., assignee of the present application), as that system is called, employs the advantages of a dead reckoning-based yardage system, with support of DGPS for calibration purposes only, and combined with the full-featured management and information capabilities of the PROLINK system. In the ACUTRAK system, the desirable attributes of a dead reckoning system are combined with limited aspects of a GPS system, through optimal estimation computer algorithms preferably using a Kalman filter, to achieve a significant synergistic improvement in performance of a golf course position, distance measurement, navigation, information, and course management system over a wide operating envelope.
The ACUTRAK system is golf cart-based, but could be packaged alternatively in smaller vehicles, even a set of golf bag wheels equipped with a mobile unit or a hand-held unit used with a pedometer version of the wheel-tracking system disclosed in the ""962 application. That system utilizes virtually all of the features of the PROLINK system disclosed in the ""295 and ""905 applications, except that the ACUTRAK system places limited reliance on DGPS, using it as a calibration technique only. In its primary functions the ACUTRAK system employs a dead reckoning system that tracks distance moved by and orientation of the wheels, extrapolated to the heading or bearing of the golf cart (or other roving unit) in which a portion of the overall system is incorporated. The ACUTRAK system is unaffected by even frequent inability to view a satellite navigation system, such as the GPS satellites, requiring only relatively infrequent calibration during play to avoid a gradual increase or buildup of error in measurements as the cart is driven about the course. Thus, instead of experiencing frequent out-of-service indications on the cart monitor, the golfer is cognizant only of continuous, reliable, highly accurate operation of the ACUTRAK system.
The principal features and technology of the ACUTRAK system are not limited to position, distance measurement, navigation, and information on a golf course. Rather, the system may be extended to many other consumer, commercial, and industrial applications of satellite navigation and digital communications technology where problems of GPS or DGPS signal loss can occur whether because of physical obstructions in the vicinity of the roving unit, line of sight problems, or interference from other, stronger signals. Indeed, the ACUTRAK system is usable in virtually any commercial endeavor where it is necessary or desirable to keep track reliably of the accurate position, distance relative to a given point, and/or navigation of a host of roving units, such as in a vehicle fleet management system, package delivery system, or other transportation system, or an agricultural planting and harvesting system, where obstructions or other interference abound.
Also, although the ACUTRAK system is preferably golf cart-based, it could be packaged alternatively or additionally in smaller vehicles, or even in or with a set of golf bag wheels equipped with a mobile unit or a hand-held unit used with a pedometer version of its wheel-tracking system. Any generic terminology used in this application, such as xe2x80x9cmobile unit,xe2x80x9d xe2x80x9cportable unit,xe2x80x9dxe2x80x9croving unit,xe2x80x9d and the like is intended to apply to any version of the system that utilizes high bandwidth dead reckoning navigation technology which is calibrated by low bandwidth satellite navigation technology. Advantages provided by the synergistic use of these technologies are enhanced by additional features and aspects which are incorporated in hardware and software to provide, for example, fixed distance measurements, in contrast to varying distance measurements resulting from the player""s (or more generally, the user""s) movement, information communication between base station and roving units, and traffic management.
In the ACUTRAK system disclosed in the ""962 application, the dead reckoning (DR, alternatively referred to as dead reckoning navigation or DRN) system is the golf cart navigator which determines distance (yardage) measurements as well as heading. Other information derived from DGPS is used solely to calibrate the DR errors in real time so that each cart is periodically calibrated and re-calibrated to survey points during play. With each calibration, accumulated DR errors are reduced such that wheel scale factor (SF) and compass misalignment errors become very small compared to the uncalibrated nominal errors. They are not completely eliminated, however, because of temperature changes, heating up of cart tires, and tilt effects on the compass. Nevertheless, the DR errors grow slowly after each calibration, so that accuracy of within approximately two yards on distance measurements for the yardage traversed on about a par 5 golf hole, which is a distance of about 500 yards, can be maintained. Generally, at some point on every fairway from tee box to green at least minimal LOS to GPS satellites is available so that calibration can be performed, and the calibration is automatic.
The distance which may be traveled with the DR navigation system of the ""962 application with highly accurate distance measurement (e.g., within two yards) is a function of the precision and sophistication of the DR sensor(s). It is possible, for example, to play an entire round of golf with only a single initial DGPS calibration for that level of yardage measurement accuracy, given a suitable DR sensorxe2x80x94but a compromise between precision/ accuracy of the product and its cost is necessary for a practical system.
Only GPS raw pseudo-range and range rate measurements are used to calibrate the DR system. Calibration of errors can be performed with fewer than four GPS satellites in LOS view to the golf cart; in fact, availability of only one GPS satellite will suffice for calibration. In the ACUTRAK system of the ""962 application, the xe2x80x9cmethod onexe2x80x9d DGPS approach of Blackwell (supra) is used to provide corrections for the GPS pseudo-range and range rate measurements. In xe2x80x9cmethod one,xe2x80x9d the base station measures the error between the estimated base station pseudo range to the GPS satellite (based on the known location of the base station GPS antenna) and the measured GPS receiver pseudo range to the GPS satellite. Errors in the range rate are also measured, and all raw measurement errors are computed for each satellite in LOS view of the base station antenna. The errors are then broadcast to the roving units so that the roving unit GPS receivers can subtract each satellite pseudo range error from each satellite pseudo range measurement. The roving unit need only apply the corrections to the subset of GPS satellites being tracked by it at that particular time. The corrected pseudo range measurements for the satellites in its LOS view are then used by the roving unit GPS receiver to compute the position, velocity, time (PVT) solution that is provided to the user for navigation.
In contradistinction, the so-called xe2x80x9cmethod twoxe2x80x9d approach calls for the base station to measure the position error between the known base station GPS antenna position (latitude, longitude, and altitude) and the GPS receiver computed position (latitude, longitude, and altitude) to compute a correction in north and east position. That correction is broadcast to all roving units on the system. But since the roving unit might be looking at any subset of the total number and arrangement of GPS satellites being viewed by the base station, and the correction is unique to the specific satellites the roving unit is tracking, the base station must broadcast a north and east position correction for each and every possible combination of satellites. Clearly, this is a considerable and recurring quantity of data. The roving unit then selects the north and east position corrections corresponding to the set of satellites being tracked, and applies them to the GPS receiver latitude, longitude, and altitude output.
The requirement of substantially greater communications bandwidth for the DGPS correction information is perhaps the greatest drawback of the method two approach relative to method one. Method one also provides a xe2x80x9ccleanerxe2x80x9d solution which allows greater flexibility in selecting filtering algorithms to be employed for enhanced performance. Industry standard RTCM-104 was created to encourage and take advantage of the more efficient method one approach. In the disclosure of the ""962 application, a floated sensor compass and a single front wheel sensor are used in a preferred embodiment of the DR navigation system of the cart, with the method one DGPS technique used for calibration. The same is true of the present invention, the difference relative to the ""962 application residing in the sensor implementation.
Mechanical issues addressed in the implementation of sensors of the ACUTRAK system on a golf cart include (1) selection and mounting of the wheel sensor used for measuring distance traversed by the cart, and (2) selection and mounting of the electronic compass used for measuring bearing (direction, relative to a reference direction, typically true north). It is necessary to determine the most desirable or advantageous wheel for location of the wheel sensor on the golf cart. The rear wheels of the cart undergo slippage during rapid acceleration and braking on wet grass; hence, mounting the sensor on a rear wheel is more likely to result in errors in determination of distance traveled by the cart under those conditions. On the other hand, since the front wheels of the cart can turn, wheel velocity is computed along the direction that the wheel is pointed rather than the direction the cart frame is pointed. Resulting error may be overcome mathematically in navigation software for the ACUTRAK system, as described in the ""962 application.
Selection of a proper sensor for detecting wheel rotation involves several factors. Hall effect sensors detect the presence of magnetic fields and are sufficiently rugged to withstand outdoor extremes of temperature, moisture, and soil contamination, with a limited capability to sense fine movements of the wheel as it rotates, for higher resolution. Optical sensors possess the capability to sense extremely fine movements, but lack robustness in an outdoor environment, and are more expensive than magnetic sensors.
The ACUTRAK system disclosed in the ""962 application employs a dead reckoning system that uses a floated compass in conjunction, in one embodiment, with a wheel sensor mounted on one front wheel, with a special acceleration compensation algorithm referred to therein as xe2x80x9ccompass tilt estimationxe2x80x9d algorithm for the floated compass. It is desirable for wheel rotation resolution to be at least 64 counts per wheel revolution, i.e., to possess the capability to detect at least every 5.625 degrees of revolution. A floated compass has a sensor which is floated in a liquid bath and which uses the Earth""s gravity to keep the sensor level with respect to the gravity field, thereby resulting in the compass sensor remaining fixed with respect to the earth""s magnetic field. In this way, a floated compass allows accurate measurement of magnetic heading under various adverse conditionsxe2x80x94for example, when the golf cart is tilted on a hill.
To overcome potential loss of accuracy arising from response of the floated compass to acceleration of the golf cart (e.g., starting, braking, or turning) such that the sensor is artificially tilted throughout an acceleration event, compensation for compass errors that arise during such an event is achieved in the system of the ""962 application by high resolution wheel sensing to at least 64 counts per revolution, and an acceleration compensation algorithm run in the navigation computer to predict the effect of the induced tilt on the compass heading output. With a dual front wheel sensor configuration, even greater resolution is requiredxe2x80x94minimally about 720 counts per revolution (equating to a capability to detect at least every 0.5 degrees of revolution), because mathematical algorithms for such a configuration are highly sensitive to wheel quantization for accurate dead reckoning performance.
In an embodiment of the ""962 application system, a wheel sensor constituting a standard optical encoder is employed, with modifications designed for survival of the sensor in the hostile outdoor environment of the golf course. The modifications include encapsulating the case of the sensor in an epoxy compound to seal it against penetration and fouling by water or soil, and using a sealed bearing on the encoder shaft for the same purpose. The wheel sensor has an effective resolution of 1024 counts per revolution, and is projected to be capable of 200 million rotations without failure. In practice, however, xe2x80x9csealedxe2x80x9d bearings are something of a misnomer in that they do not filly inhibit fouling in a hostile environment. Hence, the sensor and the accuracy of the system must be subjected to frequent inspection. Servicing or replacement of the wheel sensor must be undertaken in aggravated cases. It would be desirable to provide an improved wheel sensor system, and it is a principal objective of the present invention to do so.
According to the present invention, an ACUTRAK system is implemented in part using a wheel sensor in the form of Hall effect magnetic rotation system. A floated compass is used in conjunction with the wheel sensor for accurate measurement of the rotation and the direction of rotation of the wheel. The sensor element is attached to a mounting bracket, and a magnetic strip is attached to a mounting frame. The data collected is used to measure distance traveled and cart velocity, as well as detection of vehicle motion, among other things. Unlike other types of wheel sensors, the magnetic wheel sensor is capable of providing rotation measurements in electrically and magnetically noisy environments. This is achieved in part by making the housing for the Hall effect sensors electrically conductive and grounding it to the internal sensor ground. Additionally, the Hall effect sensor assembly is electrically insulated from the chassis of the golf cart. The system generates its data output without any physical interfaces, which effectively eliminates sources of degradation attributable to friction. Moreover, the magnetic wheel sensor can be fully sealed by electrically connecting the sensor integrated circuit (IC) to a printed circuit board, inserting the board into the housing, and then potting the board and the sensor IC assembled thereon completely in place with epoxy, for example, to avoid damage from outside contaminants. Additional advantages of the magnetic wheel sensor are its relative simplicity of assembly, installation, and inspection.
According to the invention, then, apparatus is provided for installation on a golf cart to enable calculation of the distance from the cart to a golf cup, a hazard, or other feature of a hole of a golf course which has been surveyed so that the location of such feature is known, from which to make a close approximation of the distance to such feature from a golf ball in a lie proximate to the cart. The apparatus includes a dead reckoning (DR) wheel sensor arrangement for determining speed and direction (forward/reverse) of the cart relative to a tee box of the hole as a known point of origin to which the DR assembly has been calibrated. The arrangement includes a magnetic strip with a plurality of alternating magnetic poles impressed across the strip, which is attached to the rim of a mounting fixture inside the wheel well of the cart. The Hall effect sensor assembly is affixed to the axle of the wheel for detecting passage of the alternating magnetic poles on the strip during rotation of the wheel. A floated compass is attached to the cart, preferably substantially directly above this wheel, to determine the cart heading. Knowing the parameters of speed, forward/reverse direction, and heading of the cart at any given instant relative to the origin enables calculation of real-time distance from the cart to the known location of a feature of interest of the hole being played with the cart.
Selection of the cart wheel to be used for this arrangement is somewhat arbitrary, although as will be noted presently, the left front wheel of the cart is preferred. In one embodiment, the left front wheel was selected to minimize potential errors with the cart""s GPS antenna, which was mounted on the left side of the electronics module. Additionally, the driver of the cart sits in the left seat, and therefore a greater frictional force is present on the left front tire than on the right front tire.
A global positioning system receiver of the cart receives differential GPS position signals which are used to re-calibrate the DR wheel sensor assembly at least once during play of each hole to restore a level of accuracy to the calculation of distance by substantially removing error buildup arising since the previous calibration.
Using the invention, a method is provided for performing a relatively accurate calculation of the distance of the ball to a feature of interest on a hole of a golf course which has been surveyed so that the locations of various features on each hole are known. A golf cart on which a dead reckoning navigation (DRN) system is installed (including the magnetic wheel sensor assembly for determining speed and direction of the golf cart and the compass for determining heading of the golf cart during movement thereof and ultimately determining the position of the golf cart) is positioned adjacent a tee box of a hole to be played on the course, as an origin of coordinates for the relative position of the golf cart. After a tee shot, the golf cart is repositioned adjacent the new position of the ball resulting from that shot. As the golf cart is being repositioned, the coordinates of the new position of the ball relative to the origin are determined from the DRN system. Using the new position coordinates in conjunction with the known position coordinates of the cup for the hole being played, the approximate distance from the new position of the ball to the cup is ascertained. At least once during play of a hole, the DRN system is re-calibrated to restore a level of accuracy of measurements by the DRN system by substantially removing error buildup since the previous calibration of the DRN system from the determinations.
As used herein, the term xe2x80x9ccoordinatesxe2x80x9d is simply intended to refer to the location of an object regardless of the specific form of mapping or surveying, which may, for example, be of the type described and claimed in the ""295 application, and not necessarily to an X-Y plot, bit mapping, or the like.
The invention is also usable in a system for determining the precise locations of a plurality of golf carts on a golf course in real time, as the golf carts are being used during play of the golf course, for purposes of course administration and management. This task, that is, of observing the pace of play on the course and any trouble spots on a video monitor or other display, is conveniently handled at the pro shop or elsewhere in the clubhouse. There, a base station is provided which includes apparatus for wireless communication with each of the golf carts on the course, including receipt of information from each cart regarding its location as determined by an on-board navigation system for display on a course map on the monitor.
Each of the carts is outfitted with a DRN system of the type embodying the invention, with the magnetic wheel sensor assembly for determining the speed and direction of the cart, and the compass or the like constituting means for calculating the heading of the cart on the course, so as to fix the location of the cart relative to at least one known landmark of the course. The landmark may be any natural or artificial object or feature such as a marker or a tee box, whose location is known, as by course mapping, and to which the DRN system of the cart has been calibrated. In addition to the DRN system, each cart is outfitted with apparatus for wireless communication with the base station, including communication of data derived from calculations employing the DRN system which are indicative of location of the relative to at least the one known landmark. Each cart is also provided with a receiver for receiving differential global positioning system (DGPS) signals from earth satellites in unobstructed line of sight (LOS) to the cart for re-calibration of its DRN system from time to time during each round of play of the course relative to a known landmark, which might typically be the tee box location for the hole being played. In this way, the accuracy of the DRN system of the cart is restored for relatively accurate determination of real-time location of the cart on the course.